1. Field of the Invention
The present invention concerns a method for reducing a dead volume in an apparatus designed to be connected to the respiratory system of a patient.
The present invention is also directed to a device for reduction of dead volume in an apparatus designed to be connected to the respiratory system of a patient.
2. Description of the Prior Art
As a rule, when an apparatus is to be connected to the respiratory system of a patient, a machine dead volume is introduced. This dead volume results in carbon dioxide in expired gas from the patient being returned to the respiratory system with the following inspiration.
“Apparatus” as used herein relates to all respiratory apparatuses which can be connected to the respiratory system to condition respiratory gas, facilitate breathing, support breathing, control breathing, etc. Typical apparatuses of this type are respirators and ventilators for respiratory therapy treatment and anesthesia apparatuses.
“Patient” as used herein relates to all living creatures, but primarily humans and domesticated animals.
A known way to reduce reinspiration of gas mixed with carbon dioxide is described in WO 91/19526. According to the known method, gas is evacuated from the dead volume primarily during the final phase of expiration while fresh gas is concurrently provided.
A drawback with the known method is that limitations exist in the volume which can be evacuated. With the use of many components connected to the patient, for example, heat and moisture exchangers (HME), reflectors for anesthesia gas, bacteria filters, etc., the mechanical dead volume can be relatively large, 50-100 ml. This volume then approaches the same magnitude as the tidal volume—particularly if it is a child, small animal or adult with severe lung illness who is the patient.
Since the method according to WO 91/19526 is primarily directed to evacuating gas deep in the respiratory system of the patient it also requires very thin tubes. This results in significant low pressure being required to bring about a sufficient stream of evacuated gas. For obvious reasons a low pressure larger than about 1 atmosphere cannot be produced.
Therefore, a need for a method and a device for reducing a dead volume which has a broader applicability and which overcomes the problems named above exists.